It's by far the part of the game I like the least... there's always a couple of gold nuggets I can't seem to find. It's boring, and also frustrating to see my food supply dwindle.
I’ve noticed that using a teleport spell will take you to, or very near, an unexplored area. If I feel like I’ve looked everywhere that shows signs of being a false wall then I’ll use a teleport spell and that solves it for me.
Same goes for finding secret rooms in fully explored levels if I have a lot of unused teleportation spells.